Semiconductor integrated circuits typically comprise layers of stacked interconnected metal layers with dielectric materials between them to form a device, such as a transistor. Typically, a plurality of such layers are laid down on a substrate of silicon, or the like. The layers forming the device, including gates, etc., are then covered with a barrier layer, a metal layer, and finally a layer of titanium nitride, which serves as an anti-reflective coating. A pattern of photoresist material is deposited on the titanium nitride layer for providing electrical contacts with the transistor, or other device. Lithographic techniques are used to pattern the photoresist using a photo-sensitive mask.
In the event that the photoresist pattern is unsatisfactory, for example, improperly shaped, the photoresist may be reworked, i.e., removed and a fresh photoresist layer deposited.
Current photoresist rework processes use a solvent/and or an oxygen-containing plasma to remove the photoresist before starting the lithographic sequence again. Typically, the wafer on which the photoresist is deposited is subjected to an oxygen plasma at a temperature of about 250 .degree.C. to strip the photoresist. After, the stripping process, the surface is cleaned with a rework solvent to remove photoresist residues. Commonly used solvents include H.sub.2 SO.sub.4 /H.sub.2 O.sub.2 or solutions commonly known in the trade as EKC-265 (a solution comprising hydroxyl amine, 2-(2-aminoethoxy)ethanol, cathecol, and an alkaline buffer), and ACT-CMI (a solution of dimethylacetamide and diethanolamine).
The high temperatures and oxygen gas used to strip the photoresist tends to cause oxidation of the titanium nitride layer. The TiN reacts with oxygen radicals to form an oxynitride of the general formula TiO.sub.X N.sub.Y. The oxidation changes the conductivity of the TiN layer and it becomes more susceptible to contamination by mobile ions during the solvent cleaning step. Mobile ions, such as Na.sup.+, K.sup.+ Cl.sup.-, fluoride species, or other ionic inorganic compounds, tend to become incorporated into the solvent over time. If they become absorbed by the titanium nitride layer, the contaminants may travel through the various layers and cause electrical device defects and degradation in the overall performance and yield of the device.
The present invention provides a new and improved method of photoresist rework, which overcomes the above referenced problems, and others.